The present invention relates to electromagnetically operable proportional pressure control valves and more particularly to proportional pressure control valves each having a spool that is slidable depending upon the magnitude of fluid pressure in a pressure chamber for opening and closing a passage between an inlet and outlet ports of the pressure control valve.
Electromagnetically operable proportional pressure control valves are used in various fields related to automotive vehicles. One example application of this type of valve can be found in an engine cooling system wherein an oil pump is operated by such the valve and is disclosed in a Japanese Patent Publication (KOKOKU) No. 73955/1993. Refer to FIG. 2 to understand the conventional application of such a valve wherein the electromagnetically operable proporitonal pressure control valve 10 is connected in parallel to an oil passage 51 having an oil pump 50 and an oil motor 52 for selectively driving a fan 53 to cool a radiator 54. A working oil discharged from the oil pump 50 flows through the passage 51 when an inlet port 16 of the valve 10 is closed and in passages A, B through the valve 10 when ports 16, 18 open. A signal indicating the water temperature in the radiator 54 is supplied through an electrical cord 55 to ECU 56 which controls the magnitude of electrical current to be supplied to the valve 10 in response to a variation of the water temperature in the radiator 54.
A pressure control valve according to the prior art has inlet and outlet ports, a passage allowing an oil to flow from the inlet port to the outlet port, a control valve for cutting off and establishing fluid communication between both the ports, and an electromagnetically driven pilot valve to regulate the oil pressure in a first oil chamber inside the control valve to displace the control valve in response to variations in the water temperature of a radiator. The control valve is of a frustum of cone and will be subjected to fluctuating forces due to sudden changes in a pressure receiving area on the control valve when energization and disenergization are repeated at a high frequency rate.
In order to diminish the hunting of the control valve due to such fluctuating forces produced in the electromagnetically operable pressure control valve, prior pressure control valves as known in the prior art are provided with a second oil chamber that normally communicates with the first oil chamber through a spill passage.
However, the provision of the second oil chamber and the spill passage causes the valve to be complicated in structure and only offers a reduced damping effect when the oil temperature is varied and a change in the oil flow resistance is found in the spill passage.
It is therefore an object of the present invention to provide an electromagnetically operable proportional pressure control valve having a spool for cutting off and establishing fluid communication between inlet and outlet ports therein.
According to the present invention, there is provided an electromagnetically operable proportional pressure control valve comprising:
valve body means having at least one fluid inlet port and fluid outlet port and a passage for communicating between both the ports;
a spool slidably accommodated in the valve body means for opening and closing the passage between both ports and having a diametrically reduced bore;
plunger means housed in the valve body means to define a pressure chamber and having a pilot valve;
return passage means arranged through the plunger means between the pressure chamber and the outlet port; and
electrical means having an electromagnetic coil and a core of magnetic material to generate electromagnetic force for allowing the pilot valve of the plunger means to move.